Tsunami Hazards Flashcards
What can tsunamis originate from?
Displacement of the water column by:
- Earthquakes
- Slope failure/ mass movements
- Volcanic activity
- Bolide impact
What do all tsunami sources have in common?
short lived water displacement disrupting the whole water body
What is the theory behind tsunamis?
Initial displacement - (water coloumn raised, gravitational spread of disturbance)
What is the period of a tsunami?
T - time for one wave to pass a point
How is tsunami velocity calculated?
Wavelength / time
What will the disturbance from tsunamis produce?
A wave-train of multiple waves
How will tsunami waves tend to behave? (particularly sesimogenic)
Shallow-water waves (due to the length to depth ratio)
What will the length of tsunamis typically be?
~200km
What will the typical period of a tsunami wave be?
10s of minutes
What will the amplitude of tsunami waves be in open ocean?
relativeky low (e.g 1m) compared to run up amplitude
How is the velocity for shallow water waves (tsunami) calculated?
sqaure root of gravity X depth
What is the energy loss if tsunami waves proportional to?
Wavelength - longer wavelengths more effieicnt so less energy loss leading to greater diatance travelled
What happens to tsunami waves when water gets shallower?
Velocity decreases but wave period stays constant so shorter wavelength and higher amplitude
Known as Shoaling or Amplification shorewards
Can wave speed by outrun on land?
Wave still approach rapidly at a speed too fast to outrun
What will the slope of a tsunami wave be like and how does this affect its appearance?
Still relatively gentle with wavelength of several km looks like a rapidly rising wave level instead of wall of water
How will the tsunami behave based on the displcement at fault?
Side which moved up will be peak followed by trough and side which moved down will be trough followed by peak
Thailand 04 water receded first but sri lanka had no warning
What was the ffect of the tsunami travelling across the indian ocean from sumatra 04?
Travelling through deeper ocean lead to increased wavelength
Wjat are the 5 main approaches of tsunami mitigation?
- Direct warning/ monitoring
- Planning - tsunami models
- Education and awareness
- Learning from past events
- Direct protection
What was learnt for monitoring and warning post sumatra 2004?
Lack of Indian ocean wanring system (affetcing those whose didnt feel EQ)
Lack of public awarenss due to limited EQ activity/ tsunami in recent history
What is an example of a real time monitoring system for tsunamis?
DART - direct detection and warning system
Why are DART systems important?
Provide data to warn public
Accurate warning (minimise false alarms)
Direclty feed to real time models
But with time taken to recove data and then transmit to national and local scale wave might have alrady reached shore
How does the DART system work?
Presseure sensor on the sea floor which communictes the passage of a tsunami to a buoy
Not affected by normal storm waves
Where are DART systems usually placed?
On the oceanward side of faults to provide warning for areas with time to plan
What is the assumed idea for people thinking to reach safety form tsunami locally?
Will feel EQ and head to higher ground
What does effective tsunami mitigation rely on?
Alarm/ effective communication system
Local emergency plans (hazard map)
Evacuation routes
Public awareness
What was the problem with detection of P and S waves from 04 by internaitonal seimsic netowkr?
By time waves had reaches australia and reort by usgs was published saying potential for tsunami shore was already inundated
What was the main flaw of mitigation for 04 tsunami?
Aspects recognised but no confirmation of tsunami released
What can be learnt from tsunami in 04?
Syeystms need to be in place on local scale
All potentially affectd countries net to be in network
Coordination of govenremnts
Improved sensor network
How can tsunami planning via modelling be done?
Forecast parameters - rapid and accurate models with potential real time forecasts
What are the 3 stages of tsunami modelling?
Wave generation
Tsunami propagation
Inundatrion
Why is tsunami modelling done?
assesment of tsunami potential rely on data avaliable at the time with potential revision from monitoring data
How is public awareness used to mitigate tsunamis?
Use of maps and signs key to directin potential responses
Why is effective communication of tsunami process needed?
First wave not always largest (chile 1960 3rd was the biggest), potential for multiple waves over several hours
What can be learnt from past tsunami events?
Where megathrusts occur
Recurrence time
If worst case scenario has been observed
Orphan tsunamis
What is the problem with direct protection from tsunamis?
People might not be as preapred for evacuation due to faith in protection so can exacerbate the hazard
Based on worst case but what if wost case hasnt happened
How can tsunamis be directly protected against?
Infrastructure - sea walls
What was the effect of the fukishima nuclear power plant from tohoku 11?
Back up generators damaged leading to 3rd worst nuclear diaster - walls in place were 6 m but wave wave upto 13m
What is thought to have exacerbated the tsunami height around northern japan?
Underwaterlandslides increased displacment
What is the problem with non-siesmogenic tsunamis?
Not detectable so go unnoticed until wave arrives
What will the characteristics of landslide induced tsunamis be like?
Still produce large local wave (size of displacing body)
Wave height might be larger than seismogenic but not as effcient so dissipate quickly
Locally high impact but with rapid decay
Some so big might still have potential to cross ocean basins
How can volcanoes be tsunami sources?
Any submerged volcano or partially submerged or PDCs
Volcani landslides - extreme (volcanic islands)
What type of tsunami was produed by Hunga Tonga?
Meteotsunami- air pressure disturbances
Has the UK experinced tsunamis?
One ~8200 yrs ago from landsldie off norwegian continental shelf
How can underwater topography affect tsunami proporgation?
If part of wave contacts shallower water causing slowing but wave behind is still moving fast through deeper water wave is ‘pushed’ in a new direction
